Binding mechanism of anti-cancer chemotherapeutic drug mitoxantrone to DNA characterized by magnetic tweezers

Background: Chemotherapeutic agents (anti-cancer drugs) are small cytostatic or cytotoxic molecules that often bind to double-stranded DNA (dsDNA) resulting in modifications of their structural and nanomechanical properties and thus interfering with the cell proliferation process. Methods: We investigated the anthraquinone compound mitoxantrone that is used for treating certain cancer types like leukemia and lymphoma with magnetic tweezers as a single molecule nanosensor. In order to study the association of mitoxantrone with dsDNA, we conducted force-extension and mechanical overwinding experiments with a sensitivity of 10(-14) N. Results: Using this method, we were able to estimate an equilibrium constant of association K-a approximate to 1 x 105 M-1 as well as a binding site size of n approximate to 2.5 base pairs for mitoxantrone. An unwinding angle of mitoxantrone-intercalation of (sic) approximate to 16 degrees was determined. Conclusion: Moreover, we observed a complex concentration-dependent bimodal binding behavior, where mitoxantrone associates to dsDNA as an intercalator and groove binder simultaneously at low concentrations and as a mere intercalator at high concentrations.